Mechanically erasable ballpoint inks are known in the art, see: JP.56-76477; Ger. Offen. DE 3,230,473, PCT Int. Appl. WO 84 00 174; PCT Int. Appl. WO 83 01 625; U.S. Pat. Nos. 4,097,290; 4,407,985; 4,349,639; 4,329,262; 4,367,966; 4,391,927; 4,410,643; 4,508,570; 4,252,727; 3,907,694; and 4,470,079.
More specifically, U.S. Pat. No. 4,410,643 discloses an erasable ink composition which includes styrene-butadiene, carbon black, volatile and non-volatile solvents. U.S. Pat. No. 4,391,927 discloses Kraton 1107 and Kraton 1101 ink compositions. The compositions further includes a hydrocarbon solvents as well as a pigments. U.S. Pat. Nos. 4,407,985 and 4,329,262 all disclose compositions similar to the 4,410,643 patent. These patents relate to erasable inks which include styrene-butadiene. U.S. Pat. No. 4,508,570 discloses an ink composition which includes polyethylene glycol 200, ether and black dye. U.S. Pat. No. 4,252,727 relates to a composition which includes a butadiene styrene copolymer as well as carbon black. U.S. Pat. No. 3,907,694 discloses a composition which includes polyethylene glycol, ether and carbon black. U.S. Pat. No. 4,470,079 discloses an ink composition which includes styrene as well as butadiene having amino groups attached thereto. U.S. Pat. No. 4,097,290 describes a initially erasable ballpoint ink containing rubber, low and high boiling solvents, pigments, and solid lubricants (stearic and lauric acid). PCT Int. Appl. WO 83 01 625 describes erasable inks containing thermoplastic block copolymers, a "critical pigment concentration", solvent, and dioctylphthalate. Japanese application 56-76477 describes erasable ballpoint pen inks containing vinyl chloride, plasticizers, pigments and, solvents.
Various additives are well known as disclosed in European Patent Application EP 190002 A2, Japanese Patent No. 83155297, and Japanese patent No. 60047082.
European Patent Application EP 190002 A2 describes the use of fatty acid esters in flushing-resistant textile printing pastes. Japanese Patent No. 83155297 (83.08.25) describes a water thinned writing ink containing polyethylene glycol esters for ballpoint pens. Japanese patent No. 60047082 A describes an aqueous ink composition for ballpoint pen comprising dyes, water and polyoxyethylene derivatives including polyethylene glycol monopalmitate, polyethylene glycol distearate, and polyethylene glycol monooleate.
The cited application publications and patents are herein incorporated by reference.
In general, prior art erasable inks employ graphite, organic or metalorganic pigments. Conventional mechanically erasable inks containing carbon blacks require external pressure for release from ballpoint pens. The pressure causes the ink to ooz or droop from the pen during nonwriting periods which easily stains clothing and the user's fingers during handling. The use of graphite results in excessive ballpoint pen ball wear; whereas, organic dyes or metalorganic pigments lack the writing quality of inks containing carbon blacks. The poor quality is due to the inherent character of the dyes and pigments, e.g., decreased opacity or binding power. Although polyoxyethylene derivatives have been used in ballpoint inks, such prior art inks are aqueous and non-erasable by their nature.
It is, therefore, an object of the present invention to provide erasable ink compositions substantially free of one or more of the disadvantages of the prior art.